1. Field of the invention
The invention relates to a method for recording image information on a data carrier.
2. Description of the Prior Art
A known data carrier or recording medium for coloured or chromatic image information (EP0537484A1), which is used in particular as a debit or identity card, comprises a card inlay, acting as a light-diffusing background, and a transparent sheet which is arranged on said inlay and on which a colour-accepting layer is arranged. The transparent sheet serves as a substrate to which optically identifiable information can be written by the carbonisation or blackening of the sheet material with the aid of laser radiation. The colour-accepting layer can be printed in colour by the coating or introduction of colorants.
In order to record a chromatic or coloured image on this known recording medium, firstly the image information of the image to be recorded is broken down into a light/dark component and at least one colour separation, as the coloured component. The light/dark component is then written to the transparent sheet with the aid of a laser beam recorder, thereby producing the regions of a grey-shade image which are blackened to a greater or lesser extent. Afterwards, the colour separation or separations of the image information is or are superposed on the grey-shade image by appropriate colorants being applied to or introduced into the colour-accepting layer.
Although this known method makes it possible for chromatic images to be applied to data carriers in a relatively tamperproof manner, it does not afford any advantages for the visual identification of images. The visual identification results almost exclusively from the analysis of geometrical relationships and forms in the image, colours present in the image having hardly any importance for the identification of the image. In many cases it has even been demonstrated that the colours present in an image not only do not improve identification processes but even, under certain circumstances, impede them. Such effects are known for example as xe2x80x9ccolour shockxe2x80x9d in psychology. Such colour shock effects were demonstrated also in official identification test series.
However, merely producing a light/dark component for physically safeguarding a photograph or image on a data carrier not only affords no advantages in terms of official identification, but is also problematic from an aesthetic standpoint, since the brilliance of the colour information is normally vitiated to a considerable extent by black-and-white information additionally applied in the substrate. Such a grey haze can be compensated for only to a very limited extent by increasing the colour saturation in the originally applied colour information.
Taking this as a departure point, the invention is based on the object of providing a further method for recording image information on a data carrier, which makes it possible, in particular to record a brilliant colour image simply in a tamperproof manner such that it can readily be identified.
According to the invention, then, features relevant to identification are recorded on the data carrier in addition to a processed or non-processed image corresponding to an original image, which features have been obtained from the original image. In this way, it is possible to apply a complete colour image with high brilliance and resolution to the data carrier, the identifiability of the image being improved by the additional recording of features relevant to identification. If the original image is, in particular, a portrait photograph which is intended to be recorded as a so-called passport photograph on the data carrier, then the method according to the invention enables the photograph to be applied to a document serving as a data carrier in such a way that it is aesthetically acceptable to the owner of the document but at the same time it also has enhanced identifiability for official identification purposes.
Thus, the method according to the invention makes it possible to separate in particular official identification features of a photograph from the aesthetic features and introduce them into the data carrier in a physically secured manner. The advantage resides in the fact that the aesthetic configuration of the photograph, for which colour is of great importance, can be realised independently of the configuration securing the identifiability of the photograph or image, in a separate step.
The features relevant to identification are preferably obtained by a spatial analysis of the original image, the spatial analysis being applied to one or more colour separations of the original image.
It is particularly advantageous if spatial filters are used for obtaining features relevant to identification. The spatial filtering of the image information with a spatial filter or with a suitable combination of spatial filters yields the edges and lines present in the image to be recorded with the result that, after filtering, only a line drawing or a so-called xe2x80x9csketchxe2x80x9d, is present if the filter or filters used is or are chosen in a suitable manner. This line drawing or sketch already suffices in its own right to enable the image that is to be recorded to be unmistakably recognised in particular from standpoints of official identification.
For obtaining or extracting the features relevant to identification, the procedure, similar to the procedure with a caricature, is that firstly, in a first phase, the image or the image information is reduced by iterative omission of non-essential details, that is to say of details which do not promote, or even obstruct, the identifiability. In a second phase, the reduced information is then transformed in such a way that it can be realised physically visibly in the most economical manner possible.
In order then to improve the human identifiability of faces with a simultaneous reduction in the data, the invention provides for a line drawing to be obtained from the original image as features relevant to identification, which line drawing is realised in the course of the buffer-storage and/or in the course of the recording of the image on the data carrier, in particular in vectorized form.
In order to improve the identifiability of a human portrait at the same time as the aesthetic impression, it is expedient if the features relevant to identification are superposed on the recorded image with register accuracy.
In an expedient development of the invention, it is provided that after the image has been recorded, its position on the data carrier itself is acquired and the features relevant to identification are recorded on the data carrier in accordance with the acquired image position. This makes it possible for the image that is to be recorded and the features relevant to identification to be recorded on the data carrier in a particularly simple manner, in particular with congruence exhibiting register accuracy, without special alignment or orientation markers having to be provided for this purpose on the data carrier.
It is particularly expedient if in order to improve the visibility of the features relevant to identification, the recorded image is the original image whose colour and/or spatial information content has been transformed or reduced in a suitable manner.
In order to further improve the tamperproofness, it may be provided that the line drawing is transformed or integrated into a security background of the data carrier.
A further possibility is for the features relevant to identification to be recorded on the data carrier with no direct spatial reference to the recorded image.
The features relevant to identification which are obtained from the original image can thus be recorded on the data carrier in different ways, where the respective ways can be applied individually or in combination. By way of example, it is possible both to integrate the features relevant to identification which are present as a line drawing into the security background of the data carrier and to superpose them with register accuracy with the portrait photograph. Recording without a direct spatial reference can also be combined with register-accurate recording and/or integration of the features relevant to identification into the background.
If the features relevant to identification are intended to be applied to the data carrier only as a sketch without direct spatial reference to the recorded photograph, then it is particularly advantageous if the features relevant to identification are recorded on a special region of the data carrier which has been prepared for the realisation of double- or tilted-image effects.
In order to improve not just the tamperproofness of the data carrier but the data protection in its entirety during the production of the data carrier or document, it is provided that after the image has been recorded, its image information is acquired in order to determine therefrom the features relevant to identification which are to be recorded in addition to the image.
In an advantageous refinement of the invention, the image is applied to an image-carrying area, suitable for the application of information, of the data carrier having a substrate, and the features relevant to identification are written to the substrate with the aid of radiation.
This procedure is particularly advantageous if, by way of example, passport photographs or other images which individualize the data carrier and are stored in a central data memory are intended to be recorded on the data carrier in corresponding peripherals. Since the whole image information is firstly applied as a colour image, the data link to the central data memory or computer can be terminated after the coloured image has been applied. The determination and writing of the image features relevant to identification that are to be additionally written can then be carried out in the peripheral, without this necessitating a data link that may adversely affect the security of the data. A further advantage is that that portion of the total image which is intended to be additionally recorded correlates particularly exactly with the total image content.
In a further refinement of the invention, it is provided that the radiation used for recording the features relevant to identification not only causes blackening of the substrate but also alters the previously applied image in a controlled manner, by evaporation or combustion, in order, in this way, to visually emphasize the features relevant to identification.
On the other hand, it is also possible for the features relevant to identification which are recorded under the previously applied image by means of radiation in the substrate to be written, without destroying the recorded image, through the latter to the substrate.
The recording of the desired image information can be realized in a particularly simple manner when the features relevant to identification are written to the substrate by means of laser radiation, preferably by means of infrared laser radiation.
A further refinement of the invention is distinguished by the fact that the features relevant to identification are used to produce further effects, such as e.g. water marks or the like.
It is particularly expedient if the image-carrying area is produced by coating the substrate provided for the recording of the features relevant to identification.